1. Field of the Invention
The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and separators alternately. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. Further, the present invention relates to a fuel cell stack formed by stacking the fuel cells.
2. Description of the Related Art
Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (unit cell). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, a predetermined numbers of the unit cells and the separators are stacked together to form a fuel cell stack.
In the fuel cell, an oxygen-containing gas or air is supplied to the cathode. The oxygen in the oxygen-containing gas is ionized at the interface between the cathode and the electrolyte, and the oxygen ions (O2−) move toward the anode through the electrolyte. A fuel gas such as a hydrogen-containing gas or CO is supplied to the anode. Oxygen ions react with the hydrogen in the hydrogen-containing gas to produce water or react with CO to produce CO2. Electrons released in the reaction flow through an external circuit to the cathode, creating a DC electric energy.
For example, the electric energy generated in the electrolyte electrode assembly is transmitted to terminal plates through a current collector provided in the separator. Therefore, the desired contact state between the current collector and the electrolyte electrode assembly needs to be maintained. However, variation in the height of the current collector or the thickness of the electrolyte electrode assembly occurs easily due to factors such as fabrication accuracy. In particular, since the rigidity of the current collector is high, the electrolyte electrode assembly may be damaged undesirably.
In an attempt to address the problem, for example, Japanese Laid-Open Patent Publication No. 2001-68132 discloses a solid oxide fuel cell. As shown in FIG. 21, according to the disclosure of Japanese Laid-Open Patent Publication No. 2001-68132, a plurality of solid oxide fuel cells 1 are stacked together. The solid oxide fuel cell 1 includes a flat unit cell 2, a first spacer 3, a second spacer 4, and a current collecting plate 5. The current collecting plate 5 includes a flat metal plate 6, and metal thin plates 7 provided on both surfaces of the flat metal plate 6. Projections 7a are formed on the metal thin metal plates 7. The projections 7a contact the surface of a fuel electrode or an air electrode of the unit cell 2.
According to the disclosure, the projections 7a have the suitable elasticity. Therefore, even if an excessive force is applied to the projections 7a, the projections 7a are deformed suitably, and absorb the applied load for preventing the damage of the fuel electrode or the air electrode which contacts the projections 7a. 
However, in Japanese Laid-Open Patent Publication No. 2001-68132, the current collecting plate 5 includes the flat metal plate 6 and the metal thin plates 7 attached on both surfaces of the flat metal plate 6. The metal thin plates 7 provided on both surfaces of the metal plate 6 have the projections 7a, respectively. Since the thin metal plates 7 have the elasticity, the surface pressure is small at portion of the current collector which is deformed to a small extent, and the surface pressure is large at portion of the current collector which is deformed to a large extent. Thus, the surface pressure in the current collector is not uniform.
Further, though the elasticity of the thin metal plates 7 is utilized, the elasticity may be lowered by the influence of heat or the like. Thus, the desired stress absorption function may not be achieved.
Further, deformation of the metal thin plates 7 due to the change in the elasticity would result in the non-uniform shapes of the respective fluid passages. In this case, it is difficult to achieve the uniform flows of the reactant gases or the like.